In electrophotographic image forming apparatuses, such as copying machines and printers, a photosensitive drum is widely used as an image bearing member. An image forming operation using a photosensitive drum is generally performed as follows. A surface of the photosensitive drum is uniformly charged to a predetermined potential by a charging device. When the surface of the photosensitive drum is irradiated with LED light from an exposure device, the potential thereon partially attenuates to form an electrostatic latent image of a document image on the surface of the photosensitive drum. By developing the electrostatic latent image with a developing device, a toner image is formed on the surface of the photosensitive drum. The toner image is transferred onto a sheet when the sheet passes through a transfer region where the photosensitive drum and a transfer member are in contact with or adjacent to each other. Instead of being directly transferred from the photosensitive drum, the toner image may be transferred onto the sheet via an intermediate transfer member.
In such an image forming apparatus, after the toner image is transferred onto the sheet or the intermediate transfer member, a small amount of toner may not be transferred. Thus, an amount of toner may remain on the surface of the photosensitive drum. The residual toner adhering to the surface of the photosensitive drum interferes with the next image forming operation, and therefore needs to be cleaned off. Currently practiced cleaning methods for cleaning the photosensitive drum include: moving the residual toner onto a surface of a rotating member, such as a roller or a rotating brush, by pressing the rotating member against the surface of the photosensitive drum, or scraping off the residual toner by using a blade in contact with the surface of the photosensitive drum to scrape a surface of the photosensitive drum, or removing the residual toner by a combination of the above methods.
It is known that, when the photosensitive drum is formed of amorphous silicon, corona products easily adhere onto the surface of the photosensitive drum because of charge elimination by a charging device. If the corona products absorb water, the electric resistance of the surface of the photosensitive drum decreases, and this may distort an electrostatic latent image. In a known cleaning method for preventing this trouble, toner, in which a small amount of abrasive is mixed and which remains and adheres to a surface of a photosensitive member, is removed and collected by both a roller and a cleaning blade, and corona products adhering to the surface of the photosensitive member are cleaned off by polishing with a small amount of toner held on a surface of the roller. Polishing of the surface of the photosensitive member is also effective in preventing toner filming which impairs optical sensitivity and charging performance and in which toner components thinly adhere over a wide range on the surface of the photosensitive member.
There has been proposed a cleaning device that removes corona products adhering to a surface of a photosensitive drum with the polishing roller and the cleaning blade described above. This cleaning device includes a polishing roller (slide roller) for polishing the surface of the photosensitive drum by being in contact therewith, and a cleaning blade provided downstream of the polishing roller in the rotating direction of the photosensitive drum. The polishing roller cleans the surface of the photosensitive drum by polishing with toner directly removed from the surface of the photosensitive drum or toner removed and moved by the cleaning blade.
In this cleaning device, however, toner does not always uniformly adhere on the surface of the polishing roller in the axial direction. If the amount of toner adhering to the surface of the polishing roller is not uniform in the axial direction, the surface of the photosensitive drum is unevenly polished, and this causes cleaning failure. Accordingly, to solve this problem, a cleaning device devised to uniformly distribute (e.g., uniformized) the amount of toner in the axial direction of the surface of the polishing roller has been proposed.
In such a cleaning device, a scraper extends in contact with a lower portion of the polishing roller in the axial direction (width direction) so that residual toner removed and collected from the surface of the photosensitive drum stays at a contact portion between the polishing roller and the scraper. While this method may be able to avoid a phenomenon in which the amount of toner becomes extremely small at a portion in the axial direction of the surface of the polishing roller, it cannot be said that the method is suited for uniformly distributing (i.e., uniformizing) the amount of toner as a whole. The amount of toner staying at the contact portion between the polishing roller and the scraper depends on the operation of cleaning the surface of the photosensitive drum with the polishing roller or the cleaning blade. Thus, the toner may not be uniformly distributed (i.e., positively uniformized) in the axial direction of the polishing roller.
Hence, even in this cleaning device, toner may non-uniformly adhere to the surface of the polishing roller in the axial direction, and this may make it difficult to sufficiently polish the entire surface of the photosensitive drum.